Proto-Uralic is the unattested reconstructed language ancestral to the modern Uralic language family. The reconstructed language is thought to have been originally spoken in a small area, and then expanded across northern Eurasia, gradually diverging into a dialect continuum and then a language family in the process. The location of the area or Urheimat is not known, and various strongly differing proposals have been put forward, such as the Central Russian Upland,^{[failed verification]} but the vicinity of the Ural Mountains is generally viewed as the most likely.

According to the traditional binary tree model, Proto-Uralic diverged into Proto-Samoyedic and Proto-Finno-Ugric. However, reconstructed Proto-Finno-Ugric differs little from Proto-Uralic, and many apparent differences follow from the methods used. Thus, Proto-Finno-Ugric may not be separate from Proto-Uralic. Another reconstruction of the split of Proto-Uralic has three branches (Finno-Permic, Ugric and Samoyedic) from the start.

In the early 21st century, these tree-like models have been challenged by the hypothesis of larger number of proto-languages giving an image of a linguistic "comb" rather than a tree. Thus, the second-order groups of the Uralic phylum would then be: Sami, Finnic, Mordvinic, Mari, Permic, Hungarian, Mansi, Khanty and Samoyedic, all on equal footing. This order is both the order of geographical positions as well as linguistic similarity, with neighboring languages being more similar than distant ones.

Similarly to the situation for Proto-Indo-European, reconstructions of Proto-Uralic are traditionally not written in IPA but in UPA.

Proto-Uralic had vowel harmony and a rather large inventory of vowels in initial syllables, much like the modern Finnish or Estonian system:

Sometimes a mid vowel *e̮ /ɤ/ is reconstructed in place of *i̮, or a low back rounded *å /ɒ/ in place of *a.

There were no monophonemic long vowels nor diphthongs, though sequences of vowel and semivowel within a single syllable (such as *äj) could exist.

Vowel inventory in non-initial syllables was restricted: only a two-way contrast of open and non-open vowels is incontestably reconstructible. The actual realization of this contrast is a question of debate: one view considers this two archiphonemic vowels ⫽a⫽ and ⫽i⫽, realized as four allophones [æ ɑ], [i ɯ] as per vowel harmony. However, other scholars such as Zhivlov posit the existence of disharmonic *i-a stems in Proto-Uralic, which would imply that vowel harmony was not allophonic.